Steam generator control

ABSTRACT

A steam chamber and heater for generating steam to fill said steam chamber in combination with a control system therefor. The control system automatically energizes the heater in response to a combined signal, incorporating both temperature and pressure measurements, when the combined signal is below a predetermined level and automatically deenergizes the heater when the combined signal exceeds said predetermined level. The control system also deenergizes the heater in response to signals indicating maximum individual predetermined levels of temperature or pressure, and thereby acts as a temperature and pressure override safety system. Deenergization of the heater by one of the override controls requires manual reenergization of the heater.

United States Patent 91 Shulz I [52] US. Cl. ..236/92 R, 219/332,236/26, 236/78 A, 337/300 [51] Int. Cl. ..Gd 16/02, GOSd 27/00 [58]Field of Search.236/26, 26 A, 46 A, 78 A, C, 236/15 B, 92, 21, 76, l E;219/332, 496; 337/300, 310, 315, 308, 2, 312; 21/94; 13/31 [56]References Cited UNITED STATES PATENTS 2,126,384 8/1938 Haines ..236/76X 1,936,324 11/1933 Carson, Jr. 236/76 X Feb. 13, 1973 2,671,838 3/1954Senm ..337/3l7 2,596,704 5/1952 Malutich ..337/3l7 PrimaryExaminerWil1iam E. Wayner AttorneyLawrence B. Biebel, Nathaniel R.French, Dailey L. Bugg, Joseph G. Nauman, Gilbert N. Henderson, Mario A.Martella, Edward P. Forgrave and Thomas W. Flynn [5 7 ABSTRACT A steamchamber and heater for generating steam to fill said steam chamber incombination with a control system therefor. The control systemautomatically energizes the heater in response to a combined signal,incorporating both temperature and pressure measurements, when thecombined signal is below a predetermined level and automaticallydeenergizes the heater when the combined signal exceeds saidpredetermined level. The control system also deenergizes the heater inresponse to signals indicating maximum individual predetermined levelsof temperature or pressure, and thereby acts as a temperature andpressure override safety system. Deenergization of the heater by one of2,804,525 8/1957 Mantz ..200/140 the override controls requires manualreenergization 3,352,987 11/1967 Machado et a1 ..337/310 of the heater.1,975,851 10/1934 Kimball 236/92 X 2,026,596 1/1936 Ross ..2l9/496 X 6Claims, 2 Drawing Figures 68 I 136 363818 6234 J 5 7 4 q q F 63 5 ac/IZW z 116 IAIENTEBIEIIILIIOH 3.716.188

FIG. I I56 IIO 44 4e 40 as 29 INDICATOR I60 2 LIGHTS a I FIG HEATER ISUPPLY 32 SWITCH 36 9.2. I54 CQNTRQLLER i STEAM GENERATOR CONTROL CROSSREFERENCE TO RELATED APPLICATION This is a division of application Ser.No. 765,351, filed Oct. 7, 1968, entitled Autoclave now US. Pat. No.3,571,563, issued Mar. 23, 1971.

This invention relates to apparatus for accurately controlling thetemperature and'the pressure of the steam or other vapor within achamber during it operation.

The present invention will be disclosed with reference to its use insteam autoclaves for sterilizing medical supplies such as instruments,dressings, and other items. However, it is not limited to such anapplication and may be used advantageously to control the temperatureand pressure of the steam within chambers that are intended for otheruses.

One type of autoclave that may be used for sterilizing includes asterilizing chamber, a source of water, a heater, and a steam condenser.The items that are to be sterilized are placed within the sterilizationchamber. A measured amount of water is then introduced into the chamberwhich is hermetically sealed. The water is heated to generate the steamwhich fills the chamber. At the conclusion of the sterilizing operation,the steam is evacuated from the sterilizing chamber. The chamber maythen be opened and the sterilized items removed.

Some sterilizing autoclaves are provided with automatic controls forcontrolling their heaters. These controls turn off the heater when thesterilization temperature is reached or in the event of a malfunction ofthe autoclave that results in excessive temperatures. Also, apparatushas been provided to indicate visually or audibly the completion of thesterilization operation or a malfunction of the autoclave.

The indicators or heater controls have been operated in response to atemperature sensitive element mounted within the sterilization chamber.ln some prior art devices, the heater is automatically turned off at apredetermined temperature and may be automatically turned on when thetemperature falls below this predetermined temperature.

In these autoclaves a malfunction detector may provide a separateindication at a temperature higher than the sterilization temperatureand may disconnect the heater at this temperature. Ordinarily thedisconnected heater will remain off until manually reconnected.

Temperature control devices for autoclaves frequently include atime-interval counter rather than a The timeJnterval' temperaturesensitive device. counter is preset to the period of timethat itnormally takes to fill the sterilization chamber with steam and to raisethe temperature to the'proper level for sterilization. The time-intervalcounter is started when the heater is turned on, and turns the heateroff after the expiration of its preset time interval. It may alsoactivate an indicator after the sterilization operation hasbeen-completed.

The above-mentioned heater controls and indicators have somedisadvantages that stem from their reliance on temperature alone or onthe expiration of a period of time to determine when the heater shouldbe turned off, the indicators activated or other measures taken. Theamount of time required to reach the proper temperature will varydepending on such factors as the starting temperature of the water andthe resistance of the heating element. These variations limit theaccuracy of controls that rely only upon the time normally required tofill the sterilization chamber with steam.

Similarly, many temperature measuring devices utilize materials thathave a high temperature coefficient of expansion and measure thetemperature by monitoring the dimensions of these materials. However,the amount of change in the size of these materials is slight as thetemperature changes. The accuracy of controls that rely on such changesin size is limited because of their low magnitude. Motion transmittingdevices are sometimes coupled to these materials to provide an outputmotion proportional to the change in dimension of thetemperature-sensitive material but greater in magnitude. These motiontransmitting devices reduce the accuracy of the temperature measurement.

Moreover, the temperature sensitive element or the elapsed time countermay malfunction, causing the sterilization chamber to-become overheated.Also the autoclave may contain an insufficient amount of water or nowater at all at the start of the sterilization operation. Under thesecircumstances the sides of the sterilization chamber and the items inthe chamber absorb an excessive amount of heat before the temperaturesensitive device is activated. This happens because the temperaturesensitive device is calibrated to operate in a chamber filled with steamunder pressure. If there is no steam or an insufficient amount of steam,it absorbs heat slower than where the steam is present and in contactwith the element itself. For this reason, the lack of sufficient waterin the autoclave may result in serious overheating.

SUMMARY OF THE INVENTION In accordance with the above and furtherobjects, a control for an autoclave is provided, having atemperature-sensitive expansion unit, a pressure-sensitive expansionunit, a temperature control unit, and an over temperature-pressurecontrol unit. These units cooperate to provide a controller thatoperates in accordance with the relationship between the temperature andpressure of steam in a closed system. At temperatures above 212Fahrenheit, the vapor pressure of the steam in the closed systemincreases as the temperature increases. By measuring both the steamtemperature and the steam pressure with they temperaturesensitiveexpansion unit and the pressure-sensitive expansion unit respectively,the controller derives an accurate signal at the sterilizationtemperature from the temperature control unit and also obtains twoindependent safety checks against over heating from the overtemperature-pressure control unit.

The temperature control unit and the over temperature-pressure controlunit each include a different pair of relatively movable sections, withone section of each pair being moved by the temperature-sensitiveexpansion unit, and the other section of each pair being moved by thepressure-sensitiveexpansion unit. The two sections of the temperaturecontrol unit are brought into contact with each other by thetemperature-sensitive expansion unit and the pressure-sensitiveexpansion unit at a preset value of steam pressure and temperaturewithin the steam chamber of the autoclave. The use of two independentlymovable sections increases the accuracy of measurement by increasing theamount of motion over thatobtainable from a single section.

When these two sections are brought into contact, the heater of .theautoclave is turnedoff so that the temperature in the steam chamber doesnot exceed its preset value. After the steam has cooled below thisvalue, the heater isagain turned on until the sterilization operation iscomplete. On the other hand, the two sections of the overtemperature-pressure unit are brought into contact whenever either thetemperature or the pressure, but not both, are indicated as beingexcessively high. When these two sections are brought into contact, theheater is also turned off, and cannot be turned on until a manual resetbutton is depressed. The two sections of the over temperature-pressureunit are brought together when the temperature is excessively high, eventhough there may be no steam or insufficient steam in the steam chamberof the autoclave. These two sections are also brought together when thesteam pressure is excessively high, but the temperature sensitiveexpansion unit does not detect the high temperature.

In summary, the temperature control unit is activated only at apredetermined value of temperature and pressure to indicate that thepreset temperature has been reached, while the over temperature-pressureswitch is activated by either of two abnormal conditions: (1) thedetection of a high temperature and low steam pressure; or (2) thedetection of a low temperature and high steam pressure.

The invention and other attendant objects and ad vantages thereof willbe better and more fully understood from the following detaileddescription when considered in connection with the accompanying drawingsin which:

FIG. 1 is a longitudinal sectional view taken through the controller ofthis invention; and

' FIG. 2 is a diagrammaticview, partially in section showing therelationship of the control unit of this invention with the steamchamber of an autoclave.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a longitudinalsectional view of a monitor inaccordance with this invention is shown,having a temperature bulb 10, a hollow main housing 12, and a pressurebellows housing 14. The hollow interior of the main housing 12 isprotected by six walls, four of which l6, 18, 20, and 22 are shown; thehollow interior of the pressure bellows housing 14 is also protected bysix walls, four of which 24, 26, 28, and 30 are shown.

The temperature bulb 10 is mounted within the steam chamber 32 (FIG. 2)of an autoclave, and includes within its hollow interior a liquid thatexpands as its temperature expands. This liquid is able to flow into thehollow interior of a temperature bellows 34 through a hollow tube 36that communicates with the interiors of the temperature bulb l and thetemperature bellows 34; The temperature bellows 34 is within the mainhousing 12. To connect the bulb to the bellows 34, the tube 36 passesthrough an aperture 38 in the wall 16 ofthe main housing 12. I

The hollow interior 40 of the pressure housing 14 communicates with theinterior 42 of the steam chamber (FIG. 2) through the hollow conduit 44which has a port 46 opening into the space 40 and a port 48 1 (FIG. 2)communicating with the hollow interior 42 of the steam chamber 32.

In accordance with an important feature of this invention severaloperating elements are mounted within the chamber 15 of the main housing12. These elements consist of a temperature-sensitive expansion unit, apressure-sensitive expansion unit, a temperature control unit, and anover temperature-pressure control unit. The temperature control unit andthe over temperature-pressure control unit each comprise a pair ofsections, one section of each pair being mounted to a portion of thetemperature-sensitive expansion unit and the other section of each pairbeing mounted to a portion of the pressure sensitive expansion unit. Asthe temperature increases, the temperature sensitive expansion unitmoves one section of the temperature control unit and one section of theover temperature-pressure control unit towards the pressure-sensitiveexpansion unit; as the pressure increases, the pressure-sensitiveexpansion unit moves the other section of the temperature control unitand the other section of the over temperature-pressure control unittowards the temperature sensitive expansion unit.

The temperature-sensitive expansion unit includes a cantilever arm 50having a first flat section 52, and a second flat section 56, orthogonalto the section 52. The first flat section 52 includes an aperture 54.One end 58 of the flat section 52 is positioned in proximity with theinner side of the wall 16. A hinge 60 has one side 63 welded to theinner side of the wall 16 and the other side 65 welded to one side ofthe flat section 52 adjacent to the end 58 to mount the cantilever arm50 to the wall 16. With this mounting, the cantilever arm 50 forms aresilient support which may move with respect to the wall 16 so that theend 56 is either closer to the pressure sensitive expansion unit orfurther away from the pressure sensitive expansion unit.

The flat section 52 of the cantilever arm 50 is supported by thetemperature calibration unit 66. This unit includes a knurled controlknob 68, which is positioned above the wall 18, and mounted to the topend of the threaded shaft 70. The threaded shaft threadably engages thetapped central aperture 72 of a bushing 74, which bushing has a shoulder76 abutting the top of the wall 18 and a lateral surface 78 parallel tothe threaded central aperture 72 and abutting the sides of the circularaperture through the wall 18. The bottom side of the shaft 70 passesthrough the aperture 54 and terminates in a shoulder 80. A helicalspring 82 circumscribes the shaft 70 between the shoulder 80 and thebottom side of the flat portion 52 of the cantilever arm 50.

The temperature-sensitive expansion unit is calibrated by means of thetemperature calibration unit 66. As the knob 68 is turnedcounter-clockwise, the shoulder 80 moves closer to the bottom side ofthe flat portion 52 of the cantilever 50. This increases the compressivetension of the helical spring 82 between the shoulder 80 and the flatportion 52 of the cantilever 50. In this manner the cantilever 50 issupported and biased away from the pressure sensitive expansion unit byturning the knurled control know 68 in a clockwise direction. The topsurface of the wall 18 is calibrated to correspond to an arrow marked onthe knurled knob 68 to indicate positions of the knurled knob 68 withrespect to temperatures within the interior 42 (FIG. 2) of the steamchamber 32. The setting of the knob 68 determines the temperature atwhich the heater 184 (FIG. 2) of the steam chamber 32 is to be turnedoff to terminate a sterilization operation or to maintain thetemperature below a preset'limit for a period of time that is controlledby an external timer.

The liquid filled bellows 34 is also part of the temperature sensitiveexpansion unit. It is mounted to the wall 18 between the wall 18 and theflat portion 52 of the cantilever arm 50 with its base 62 rigidlyconnected to the wall 18 and its moveable driving surface 64 in contactwith one side of the flat portion 52 of the cantilever 50. In thisposition, the bellows 34 pushes the cantilever 50 towards the pressuresensitive expansion unit as the temperature within the interior 42 (FIG.2) of the steam chamber increases.

The pressure housing 14 forms part of the pressure sensitive expansionunit. It is mounted outside of the wall 22, with the wall 30 placed incontact with the wall 22. The interior 40 of the pressure housing 14communicates with the interior of the steam chamber 42, and includes apressure bellows 84, having its opened end spaced against the wall 30and its side wall held by the four walls orthogonal to the wall 30,which include the two walls 24 and 28.

The bellows 84 is compressed in response to increases in pressure in theinterior 42 of the steam chamber 32 (FIG. 2). The flat top portion 88 ofthe pressure bellows 84 is rigidly connected to a cylindrical housing90, which housing passes through two aligned apertures 92 and 94 in thewalls 30 and 22, respectively. The other end of the cylindrical housing90 is rigidly attached to and supports the flat cylindrical drive plate96. This drive plate is mounted orthogonally to the longitudinal axis ofthe cylindrical housing 90 and parallel to the wall 22 to move towardthe temperature-sensitive expansion unit within the interior of thehousing 12 as the pressure in the steam chamber 32 increases and to moveaway from the temperature sensitive expansion unit as the pressureinside the steam chamber 32 decreases. A cylindrical bar 98 is insertedlongitudinally through a central circular aperture 100 and through thedrive plate 96 to fit inside the cylindrical aperture 102 along thelongitudinal axes of the cylindrical housing 90 in communication withthe interior 15 of the main housing 12. A helical compression spring 104resiliently biases the bar 98 against the bottom of the cylindricalaperture 102 within the housing 90.

' A rectilinear compartment is formed within the interior 15 of the mainhousing 12 by the bent metal plate 106, which plate has a first flatportion 108 perpendicular to the wall 22' and passing from one side tothe other 116, respectively. The flat portion 114 may be welded orbolted to the wall 22 and the flat portion 116 to the wall of the mainhousing 12.

The temperature control switch of the monitor includes a first sectioncomprising a first electricalpushbutton switch 118, which may be of theMicroswitch type, having a pushbutton 120, and being mounted against theflat part 56 of the cantilever arm 50 to be moved towards the pressuresensitive expansion unit as the temperature within the steam chamber 32increases. The other section of the temperature control unit includes aspring-loaded plunger comprising the bar 98, the spring 104, and thecylindrical housing 90. The bar 98 protrudes through an aperture 122 inthe flat plate 110, and has one end 124 aligned with the pushbutton 120of the pushbutton switch 118. A radial shoulder 126 is mounted aroundthe peripheral surface of the bar 98 underneath the plate to contact theplate 110 and to restrain the bar 98 against the spring 104 as thepressure within the steam chamber 32 increases beyond that correspondingto the temperature necessary for sterilization. The shoulder 126 islocated so that it approaches the plate 110 when the pressure within theinterior 42 of the steam chamber has a value corresponding to thetemperature necessary for a sterilization operation and the steamchamber 32 has a sufficient amount of water available to create steam.

The pivot arm 50, carrying the switch 118 thereon, and acted upon by thetemperature sensor devices which include bulb l0 and bellows 34,together with the rod 98 which is acted upon by the pressure sensorincluding bellows 84 and the pressure pipe 44, functions as adifferential actuating means for the switch 1 18. Increase intemperature produces a clockwise motion of arm 52 bringing the pushbutton of the switch closer to the tip 124 of the rod 98, whilecontraction of bellows 84 due to increased pressure causes the rod 98 torise and decrease the distance which the switch must move to be actuatedby the rod. Thus, the response of this portion of switch 118 to turn thepower on and off to the heater, depending upon the combination oftemperature and pressure conditions within the chamber.

The over temperature-pressure unit also includes two sections. The firstsection comprises a pushbutton switch 130, which is mounted to thepushbutton switch 118 to move therewith. The pushbutton switch 130 hasan actuating pushbutton 132 and a reset button 134. An externalmanually-operated reset button 136 is mounted in an aperture 138. Whenthe cantilever arm 50 is positioned at its room temperature relatedposition, the manual button 136 is adjacent to the reset button 134 ofthe pushbutton switch 130. The cantilever arm 50 is in this normalposition when the temperature in the steam chamber 32 is near roomtemperature. At this time the pushbutton 130 may be reset by depressingthe button 136.

The other section of the over temperature-pressure switch includes asafety plunger 140. The safety plunger 140 includes a cylindrical headportion 142, a narrow elongated stem portion 144, and an end portion146. The stem portion 144 passes through an aperture 148 and connectsthe cylindrical head 142, which is above the plate 110, to the endportion 146, which is below the plate 110. A helical spring 150circumscribes the stern 144 between the end portion 146 and the washer152 which is held against the bottom of the plate 110. The spring 150biases the safety plunger down. The end 146 is aligned with the portionof the drive plate 96, and the head portion 142 is aligned with theplunger 132 of the pushbutton switch 130. As the pressure increasesbeyond the point where the springloaded plunger 98 is restrained by theshoulder 126, drive plate 96 contacts the end 146 of the safety plunger144 and moves the safety plunger toward the button 132 of the pushbuttonswitch 130. Consequently, when the temperature within the steam chamber32 is so low that the cantilever arm 50 is spaced away from the pressuresensitive expansion unit but the pressure in the steam chamber is high,the safety plunger 140 moves beyond the bar 98 and contacts the plunger132 of the pushbutton switch 130.

items are not properly sterilized. Also it is possible that the heaterwill raise the interior 42 of the steam chamber 32 to too great atemperature and cause damage either to the items within to be sterilizedor to the steam chamber 32 itself. This may happen because thetemperature sensitive bulb 10 does not receive as The leads 154 of thenormally closed pushbutton switch 118 and the leads 156 of the normallyclosed pushbutton switch 130 are each connected in series with theheater and the power supply for the heater 184. Accordingly, the heateris disconnected whenever the plungers 120 and 132 are depressed. Oncethe plunger 132 has been depressed, the heater is disconnected until thepushbutton switch 130 is reset by depressing the button 136. This cannotbe done until the cantilever arm 50 has returned to its normal position,indicating that the interior 42 of the steam chamber 32 is near roomtemperature.

In FIG. 2, a diagrammatic sketch of a steam chamber 32 of an autoclaveis shown, illustrating the manner in which it is inter-connected with acontroller unit 158 in accordance with this invention to control theindicator lights and the heater supply switch 160 for the au-.

toclave. In operation, water is introduced into the interior 42 of thesteam chamber 32 through the hollow conduit 162, having the entranceport 164 into the chamber 42, and being selectively closable by thecheck valve 166 within the conduit 162. After water has been insertedinto the chamber 42, the heater is turned on. The water is then boiled,filling the chamber 42 with steam. As the water boils, the steampressure within the chamber 42 increases, causing the temperature toalso rise.

The liquid-filled bulb 10 senses the increase in temperature and signalsthe controller 158; the controller 158 senses the increase in steampressure through the conduit 44. If the autoclave is operating properly,the lever 50 moves the pushbutton switch 118 downward and the pressurebellows 84 moves the bar 98 upward until the end of the bar' 124depresses the button 120 of the pushbutton switch 118. The button 120 isdepressed at the proper temperature for sterilizing the items within thechamber 42. The pushbutton switch 118 is normally closed and opens whenthe plunger 120 is depressed, disconnecting the power to the heaterwithin the unit 160 and activating a normally open relay to connectpower to an indicator light. This holds the temperature below the presetvalue. After the sterilization process is complete, the steam chamber 32is evacuated of steam and the sterilized items within are removed. Thisis done after the heater has been manually disconnected by a masterswitch (not shown) and the steam chamber has cooled.

If no water enters the chamber 42 at the beginning of a cycle, theautoclave does not operate properly. This may happen because theoperator neglects to fill the reservoir (not shown) with water, orbecause of a malfunction of the check valve l66 or for many otherreasons. Since there is no water in the chamber, the

much heat from radiation within the empty chamber as it would receivefrom direct conduction had there been steam in the chamber. Since themonitor is calibrated with the expectation that there will be steam inthe chamber, a control based entirely on temperature as sensed by thebulb 10 would permit the chamber 42 to become too hot.

The controller 158 of this invention prevents this type of malfunctionfrom damaging the chamber 42 or the items within the chamber 42. As thetemperature increases, the cantilever arm 50 is moved down. When thereis no steam in the chamber, the plunger 98 does not move up to contactthe plunger of the pushbutton switch 118. However, the button 132 of thepushbutton switch contacts the head 142 of the safety plunger 140. Thishappens at a temperature higher than that necessary for sterilization,but a temperature which is low enough so that there is no danger ofdamage to the items within the sterilization chamber 142.

When the button 132 contacts the head 142 of the safety plunger 140, itopens the circuit to the heater. The circuit remains open until thecantilever arm 50 moves back to its normal position and the reset button136 is depressed. Consequently, the heater is inactivated until thechamber 42 cools down and an operator manually resets the monitor. Whenthe nonnally closed pushbutton switch 130 opens, a normally open relayis activated to connect power to a malfunction indicating light. Thislight is within the unit 160.

If the temperature sensing system should become faulty in a systemcontrolled only by temperature, there would be danger that the steampressure would build up to a dangerous level. The heater could remain onuntil it was damaged by the steam. The high temperatures thus generatedcould damage the items within the sterilization chamber, and perhaps thechamber itself.

The controller 158 of this invention prevents this type of damage fromoccurring. If the temperature sensing element should malfunction, thecantilever arm 50 would remain in place. Consequently, the end 124 ofthe plunger 98 would not depress the button 120 of the pushbutton switch118 at the proper temperature. However, the drive plate 96 would contactthe end 146 of the safety plunger 140 and move it upward. As thepressure increased beyond the preset level, the head 142 of the safetyplunger 140 would contact the button 132 of the pushbutton switch 130.This again would disconnect the heater 184 and turn on the malfunctionindicator light.

It can be seen that the temperature and pressure controller of thisinvention controls the temperature of the steam chamber of an autoclavein accordance with a relationship between both the temperature and thepressure. It can be easily preset to a desired temperature by merelychanging the calibration for the temperature responsive part of thecontroller. On the other hand, it is able to disconnect the heater andprovide an indication in the event of a malfunction which affects eitheronly the temperature sensing portion of the autoclave or the pressuresensing portion of the monitor. Yet the monitor is reliable andinexpensive because of its simplicity.

While the invention has been described with a certain degree ofparticularity, many. modifications and variations may be made in thelight of the above teachings. It is therefore to be understood that,within the scope of the appended claims, the invention may be practicedotherwise than is specifically described.

What is claimed is:

l. A controller unit comprising: first means for sensing temperature; amovable support arm, said first means including a second means formoving said movable support to a first position at a low referencetemperature, to a second position at a predetermined second highertemperature, and to a third position at a predetermined third highertemperature; first pushbutton switch means for providing a first signalwhen positioned in said second position, said first switch means beingmounted to said movable support arm; second pushbutton means forproviding a second signal when moved to said third position; said secondswitch means being mounted to said movable support arm; apressure-sensing element adapted to be mounted in a location to bemonitored; third means adapted to move toward said first and secondpushbutton switches in response to increases in pressure sensed by saidpressure-sensing means; a first plunger resiliently mounted to saidthird means and aligned with the activating plunger of said firstpushbutton switch; said first I plunger including a restraining meansfor preventing said plunger from moving beyond the predetermineddistance, whereby said first pushbutton switch is activated by apredetermined sensed temperature and a predetermined sensed pressure; asecond plunger mounted in a line with the activating plunger of saidsecond pushbutton switch; said third means being adapted to contact saidsecond plunger and move it into contact with said activating plunger ofsaid second pushbutton switch while said first plunger is restrained bysaid restraining means and said support means is in said first position,whereby the high value of pressure will activate the second pushbuttonswitch while said temperature sensing means senses a low temperature;said first and second pushbutton switches being adapted to providefirstand second signals for monitor- 'ing purposes.

2. A controller for a steam chamber or the like comprising a firstswitch operative to provide a control signal in response topredetermined combinations of temperature and pressure conditions, atemperature sensor; a pressure sensor, differential actuating means forsaid first switch including oppositely acting members one of which isresponsive to said temperature sensor and the other of which isresponsive to said pressure sensor to cause movement of said actuatingmeans one as a result of increasing pressure and the other as a resultof increasing temperature, and a second switch also controlled by saidactuating means and operative to provide a continuing signal once theaction of either of said temperature sensor and said pressure sensorreaches a predetermined limit.

3. A controller as defined in claim 1, including means for resettingsaid second switch only after said temperature sensor and/or saidpressure sensor recedes to a condition below the predetermined limit.

4. A controller for the combined temperature and pressure of a chamber,said controller comprising a pivotally mounted arm,

a temperature responsive device operating to rotate said arm in onedirection,

a first switch carried by said arm and having an actuator button foropening and closing said first switch,

a control rod mounted for movement toward and away from said button tooperate the switch, and

a pressure responsive device connected to move said rod wherebyactuation of said switch is controlled by the combination of temperatureand pressure conditions.

5. A controller as defined in claim 4, including adjustable meansconnected to rotate said arm in the other direction for adjusting thetemperature response of said first switch.

6. A controller as defined in claim 4 including a second switch alsomounted on said arm,

said second switch having an actuating button which functions to changethe state of said second switch until it is reset and a reset button forreversing'the state of said second switch once it is changed,

a pressure limit actuator separate from said control rod and responsiveto said pressure responsive device when said device moves beyond apredetermined limit,

said limit actuator being aligned to operate said button of said secondswitch,

and a manually operated reset actuator aligned with said reset buttonand so located with respect to said arm that said second switch can bereset only within predetermined limits of pressure and temperature.

4: s t s

1. A controller unit comprising: first means for sensing temperature; amovable support arm, said first means including a second means formoving said movable support to a first position at a low referencetemperature, to a second position at a predetermined second highertemperature, and to a third position at a predetermined third highertemperature; first pushbutton switch means for providing a first signalwhen positioned in said second position, said first switch means beingmounted to said movable support arm; second pushbutton means forproviding a second signal when moved to said third position; said secondswitch means being mounted to said movable support arm; apressure-sensing element adapted to be mounted in a location to bemonitored; third means adapted to move toward said first and secondpushbutton switches in response to increases in pressure sensed by saidpressure-sensing means; a first plunger resiliently mounted to saidthird means and aligned with the activating plunger of said firstpushbutton switch; said first plunger including a restraining means forpreventing said plunger from moving beyond the predetermined distance,whereby said first pushbutton switch is activated by a predeterminedsensed temperature and a predetermined sensed pressure; a second plungermounted in a line with the activating plunger of said second pushbuttonswitch; said third means being adapted to contact said second plungerand move it into contact with said activating plunger of said secondpushbutton switch while said first plunger is restrained by saidrestraining means and said support means is in said first position,whereby the high value of pressure will activate the second pushbuttonswitch while said temperature sensing means senses a low temperature;said first and second pushbutton switches being adapted to provide firstand second signals for monitoring purposes.
 1. A controller unitcomprising: first means for sensing temperature; a movable support arm,said first means including a second means for moving said movablesupport to a first position at a low reference temperature, to a secondposition at a predetermined second higher temperature, and to a thirdposition at a predetermined third higher temperature; first pushbuttonswitch means for providing a first signal when positioned in said secondposition, said first switch means being mounted to said movable supportarm; second pushbutton means for providing a second signal when moved tosaid third position; said second switch means being mounted to saidmovable support arm; a pressure-sensing element adapted to be mounted ina location to be monitored; third means adapted to move toward saidfirst and second pushbutton switches in response to increases inpressure sensed by said pressure-sensing means; a first plungerresiliently mounted to said third means and aligned with the activatingplunger of said first pushbutton switch; said first plunger including arestraining means for preventing said plunger from moving beyond thepredetermined distance, whereby said first pushbutton switch isactivated by a predetermined sensed temperature and a predeterminedsensed pressure; a second plunger mounted in a line with the activatingplunger of said second pushbutton switch; said third means being adaptedto contact said second plunger and move it into contact with saidactivating plunger of said second pushbutton switch while said firstplunger is restrained by said restraining means and said support meansis in said first position, whereby the high value of pressure willactivate the second pushbutton switch while said temperature sensingmeans senses a low temperature; said first and second pushbuttonswitches being adapted to provide first and second signals formonitoring purposes.
 2. A controller for a steam chamber or the likecomprising a first switch operative to provide a control signal inresponse to predetermined combinations of temperature and pressureconditions, a temperature sensor; a pressure sensor, differentialactuating means for said first switch including oppositely actingmembers one of which is responsive to said temperature sensor and theother of which is responsive to said pressure sensor to cause movementof said actuating means one as a result of increasing pressure and theother as a result of increasing temperature, and a second switch alsocontrolled by said actuating means and operative to provide a continuingsignal once the action of either of said temperature sensor and saidpressure sensor reaches a predetermined limit.
 3. A controller asdefined in claim 1, including means for resetting said second switchonly after said temperature sensor and/or said pressure sensor recedesto a condition below the predetermined limit.
 4. A controller for thecombined temperature and pressure Of a chamber, said controllercomprising a pivotally mounted arm, a temperature responsive deviceoperating to rotate said arm in one direction, a first switch carried bysaid arm and having an actuator button for opening and closing saidfirst switch, a control rod mounted for movement toward and away fromsaid button to operate the switch, and a pressure responsive deviceconnected to move said rod whereby actuation of said switch iscontrolled by the combination of temperature and pressure conditions. 5.A controller as defined in claim 4, including adjustable means connectedto rotate said arm in the other direction for adjusting the temperatureresponse of said first switch.